The objective of the proposed research is to demonstrate that a new 1.9 micrometer laser can perform laser assisted vascular anastomoses of small diameter vessels (1-5 mm). The 1.9 micrometer light has optimal absorption characteristics to ensure an even deposition of energy in the vessel wall. This should result in a more desired temperature profile in the region of the anastomosis when compared with alternative sources. The proposed laser has several advantages over the more commonly used C0-2 and Ar lasers. Unlike the C0-2 laser, 1.9 pm output is transmittable through silica fiber optics, thus facilitating operative convenience and control in the sterile field. Compared to the Ar laser, the 1.9 mm laser requires lower power for welding and no irrigation to prevent tissue damage. Such a source for welding small diameter vessels can have several advantages over manual suturing, some examples of which are shorter operative times, and less foreign body reaction at the anastomosis. Phase I studies will concentrate on quantitating the influence of energy deposition using our 1.9 micrometer laser in vivo for both acute and chronic vascular welds via measurements of the tensile strength of the laser anastomoses of various vessel diameter. This will be accomplished by measuring the burst pressure of the lased anastomoses and normalizing to that of resorbable sutured anastomosis. This normalized tensile strength parameter will yield information on the importance of matching vessel- wall thickness to the tissue penetration depth of the optical radiation. A low power, compact 1.9 um laser, which will require innovation to scale down from our current system, will be designed, fabricated, and tested in vivo in Phase II specifically for clinical welding